Friday 7 September 2012 03.05 EDT
First published on Friday 7 September 2012 03.05 EDT

French police believe a deeply traumatised four-year-old girl who hid for eight hours under the bodies of her slain relatives, and her critically injured sister may hold the key to the gruesome murder of four people in an Alpine beauty spot.

The two girls were under extremely high protection as police hunted for the gunman who shot dead her parents and grandmother as well as a passing cyclist on Wednesday afternoon in what officials described as an "act of gross savagery".

Three of the four victims were shot in the middle of the head with a semi-automatic pistol meaning the killer pulled the trigger for each shot, leading to fears the professional nature of the attack may indicate a contract killing. Police said they were not sure how the fourth person, believed to be the children's mother, died.

The four-year-old, named in Britain as Zeena al-Hilli, asked for her family after she was finally pulled from the scene of carnage, "terrorised, motionless, in the midst of the bodies", said a French official. British consular officials, despatched from Paris, were trying to comfort her and her older sister Zainab.

The dead man, who was found slumped over the steering wheel, has been named as Iraqi-born engineer Saad al-Hilli, 50, from Claygate in Surrey, but there was no official confirmation of his identity or those of the two women shot while sitting in the back of the car. One of them was reported to be carrying an Iraqi passport and the other a Swedish passport.

French police guard the road to the murder scene at Cheverlaine near Annecy in the Haute-Savoie region of south-eastern France. Photograph: Chris Ison/PA

Their bodies were found in a British-registered BMW estate car near the picturesque village of Chevaline in the French Alps near where they had been camping.

French police refused to rule out any motive for the killings but described it as a "strange modus operandi" and said they had "plenty of ideas, but no real leads". Eric Maillaud, the public prosecutor, said: "At the moment we cannot say what happened, except four people were killed, or why. It's not that we have no idea; we have many ideas, many hypotheses, all of which are being looked at, but there are no real leads at the moment. My worry is that we may never find the killer."

The body of French cyclist Sylvain Mollier, a local man and father of three children, who was on paternity leave, was found nearby.

The car engine was still running when a former Royal Air Force officer came across the vehicle whose windows had been shattered by bullets shortly before 4pm on Wednesday. He first spotted the body of the elder girl, who had been violently beaten to the head and left for dead near the car and, seeing she was still breathing, called the emergency services.

He then broke the driver's window of the car to cut the ignition and saw the three bodies in the car. Nearby, the man recognised the body of a cyclist who had overtaken him on the hill leading to the beauty spot only minutes before.

Maillaud said the man, who he would not name, was "as you can imagine, profoundly shocked".

It was not until almost eight hours later that police found the second little girl cowering in the footwell in the back of the car under the legs of the dead women, where she had not moved or made a sound.

French police remove the BMW from the scene of the murders. Photograph: Salvatore Di Nolfi/EPA

At a press conference in Annecy, police said the child was only found after holidaymakers at the camping site where the family had stayed, told detectives there were two children and not one.

"There was nothing to lead us to believe there was another human being in the car. She was invisible and completely silent," said Maillaud. "She was clearly happy to be taken into the arms of the gendarme who brought her out. She smiled and started to speak in English. Almost straight away she asked where her family was."

Lt Col Bertrand François added: "We did not search for survivors because there was never any indication there was a living person in that car. The girl was small and hiding under the legs of one of the women. She was too small to show up on a heat detector."

The elder girl, who as well as being "violently beaten" was also shot in the shoulder, was said to be in a stable condition and out of danger in hospital where doctors said they had put her into an artificial coma to aid her recovery.

The bodies of the victims will undergo detailed forensic examinations on Friday. Investigators say they will try to gently question the traumatised girl, but are unsure whether she will be able to help their inquiry. "She's only four years old. Can you imagine? This child stayed still and silent next to a dead body for eight hours," Maillaud said. "She will need to be helped and protected," he added.

The French president François Hollande said authorities will do their "utmost to find the perpetrators".

In Britain, Surrey police said they were assisting the French inquiry. If robbery is ruled out as a motive, then inquiries may focus on Hilli's background to see if there was any clue in his life and work as to why he may have been targeted.

Hilli came to Britain over 20 years ago from Iraq, settling in Claygate where he was a popular and respected member of the community.

Neighbour Jack Saltman said: "They are quite beautiful kids and so well behaved. He was an extraordinarily nice man and helpful. He was a very tactile loving father. He loved to gather the girls up and cuddle them … they would go running at him and he'd catch them in his arms and kiss them. He adored them. His wife was a delightful person and I can't think why anybody would want to harm them.

"My wife is in floods of tears, she's heartbroken. When I stop to think about it I'll cry for those little kiddies. What sort of life are they going to have now?"

The foreign office said: "Our consular officials are on the ground and providing full consular assistance. Very experienced consular staff have spent time with the youngest survivor to reassure her."

Hilli is listed as being involved with two companies. Filings at Companies House say he is director of a company called SHTECH.

The company dealt with computer aided mechanical design work, mainly in the civil aviation industry, said Hilli's accountant Julian Stedman.

Hilli set up the company in 2001 and got most of his work through industry contacts. The company was "doing well", Stedman said. "I knew he worked on [designing] the kitchen of the European Airbus."

Saad and Ikbal got married in August 2003 and had Zainab two years later.